The goal of the proposed resarch is to further the art of genetic analysis of Caenorhabditis elegans, a model organism for studying the genetic basis of animal development, chosen because of its limited size and cell number and its suitability for genetic manipulation. More specific objectives are: first, to identify genetically marked chromosome rearragements that can be used as balancers to maintain recessive lethal and sterile mutations in heterozygotes and to facilitate their subsequent manipulation; second, to use the balancers to aid in saturating sections of the genome with recessive lethal and sterile mutations and to assign the mutations to genes by complementation; third, to identify and characterize deficiencies to be used in classifying steriles and lethals; and finally, to classify the mutants by light microscopy as to developmental consequences.